The present invention relates to a shock absorber, and more particularly, to a shock absorber for achieving generally linear damping force characteristics over the speed range of the shock absorber piston.
In general, a shock absorber is used in unison with a spring between a vehicle body and an axle to absorb a variety of vibrations or shocks transferred from the road to the wheel during driving conditions, thereby improving the ride comfort and handling stability. In more detail, the shock absorber improves the ride comfort by absorbing the free vibrations of its spring. Particularly, the shock absorber generates a damping force by using the fluid flow resistance during a stroke of a piston installed in the cylinder of the shock absorber.
FIG. 1 shows a section of a conventional shock absorber. A conventional shock absorber 100 includes a cylinder connected to an axle and a piston rod 120 connected to the vehicle body. The cylinder is comprised of an outer cylinder (not shown) and an inner cylinder 110. The piston rod 120 extends into the inner cylinder 110 and connects to a piston 130 in which compression and rebound channels 131, 132 are formed. The interior of the cylinder is divided by the piston 130 to form the compression chamber 112 and the rebound chamber 114. Further, an intake valve disk 141 for opening the compression channel 131 during a compression stroke is provided on top of the piston 130, and a valve mechanism 160 for controlling the opening and closing and the opening degree of the rebound channel 132 during a rebound stroke is provided on the bottom of the piston 130.
Particularly, the valve mechanism 160 of the conventional shock absorber as described above controls the opening degree of the rebound channel 132 in low and high speed ranges of the piston, thereby generating different damping forces. The particular configuration of the valve mechanism 160 is shown in an enlarged view in FIG. 1. As shown in the figure, the conventional valve mechanism 160 includes a nut 172, a washer 174, and a plurality of valve disks 162, 164 securely fixed to the lower side of the piston 130 by means of a retainer 176. Among them, the valve disk 162 has a slit 162a, which allows fluid to flow through. The slit 162a represents the smallest opening possible, which is used in generating a low speed damping force in a low speed rebound range of the piston 130. Thus, the valve disk 162 is referred to as “slit disk” or “disk-S.” In addition, a plurality of the valve disks 164 are stacked on the bottom surface of the slit disk 162. The valve disks 164 are subjected to a bending deformation by the fluid passing through the aforementioned slit 162a in a high speed rebound range of the piston 130, this creates the largest opening possible and generates a high speed damping force.
However, in a process of generating the low speed damping force while the fluid passes through the slit 162a of the slit disk 162, the conventional shock absorber shows a nonlinear damping force characteristic, which is proportional to the square of the speed of the piston. Such a nonlinear damping force characteristic causes a damping force characteristic in a low speed range to be degraded, which deteriorates the ride comfort and handling stability of a vehicle. Further, in the conventional shock absorber the damping force in the low speed range is closely linked to the middle-high speed damping force (i.e., not enough degrees of freedom), so that if the low speed range is tuned, the middle-high range is also increased.